1. Field of the Invention
The present invention pertains to an improved detector apparatus and method for a single individual to determine top dead center of an internal combustion engine, such as a gasoline or diesel engine, unaided by a second person. The detector device is adapted to be sealably retained in the combustion port of an engine to seal the chamber. The device indicates that the piston has achieved top dead center by being audibly expelled from the port by the pressure exerted on the device when the piston reaches top dead center.
The present invention relates generally to remote determination of the dead center position of the piston in an internal combustion engine.
2. Description of Related Art
The inspection and adjustment of the valve clearance in an internal combustion engine is very important, particularly with regard to environmental pollution which is caused by exhaust gasses. Moreover, the inspection and adjusting of the valve clearance has in the past required a considerable amount of time and labor, and has had to be performed by persons, skilled in this particular area, and usually by more than one person. Likewise, adjustment of an gasoline engine's ignition spark is a crucial step in maximizing the engine's power output and efficiency, while minimizing exhaust pollutants. When an engine's spark is properly set, the engine pollutes less and operates at peak efficiency.
The ignition timing is easily adjusted by appropriate manipulation of the engine's distributor, and such adjustment is one typically undertaken by the home mechanic. Ignition timing is determined by reference to the linear position of a chosen piston, usually the number one, piston in its stroke. The top of the piston's compression stroke is the highest point in its cycle relative to the spark plug and is called "top dead center."
Both of the above described adjustments require determining when the piston is at "top dead center." In order to detect when the piston is at top dead center, a crank lever has traditionally been rotated by hand, so that the person performing the function could observe when the number one piston was at top dead center. However, since modern automobiles are in most cases equipped with a cooling pump, a power steering pump, a supercharger and the like in the engine compartment, the above-described cranking operation becomes very difficult because of the small amount of space remaining in the engine compartment. Moreover, the above-described equipment is connected to the crank shaft so that, in trying to rotate the crank shaft by hand, a great amount of force is required and frequently results in the person turning the crank injuring himself due to slipping of his hand. In high compression gasoline engines this is impossible unless all the spark plugs are removed. Diesel engines normally can not be hand cranked at all.
Because top dead center occurs at the end of the piston's compression stroke, top dead center in the combustion chamber is accompanied by a maximization of the pressure within the chamber. After establishing top dead center, ignition timing is indicated in degrees before or after top dead center. Thus, the first step in adjusting ignition or vavle timing is to rotate the engine crankshaft and determine the point of the piston's closest approach to the spark plug or top dead center. However, as indicated above, rotating the crankshaft of a modem engine requires more force than a person can practically generate, and so engine rotation is usually done by actuating the electric starter motor with the ignition switch. Therefore, measuring top dead center traditionally requires two people, one to operate the starter switch, and one in the engine compartment to measure piston position. Various devices for measuring top dead center are found in the art.
U.S. Pat. No. 1,535,688 teaches a device to measure the pressure in a combustion chamber and thereby indicate top dead center. This device measures the combustion chamber pressure by means of a guage inserted into the spark plug port. One embodiment visually indicates top dead center by measuring the pressure maximum in the sealed combustion chamber through a flexible diaphragm mechanically attached to an indicator needle. Another embodiment audibly indicates top dead center on an unsealed chamber via a pair of whistles, one which is actuated by the compression leading up to top dead center and the other which is actuated by the suction following top dead center. The embodiment with the gauge requires a delicate and precision mechanism to measure top dead center, and the embodiment with the whistles is a complicated and expensive apparatus.
U.S. Pat. No. 2,098,058 reveals a mechanism to visually indicate top dead center by measuring the pressure maximum in the sealed combustion chamber with a manometer through a spark plug port. The manometer mechanism is fragile and requires various pressure release valves to protect against its damage.
U.S. Pat. No. 2,511,392 demonstrates an instrument which visually indicates top dead center by illuminating a light bulb through an electrical connection between the piston and a slidable rod. The slidable rod is mounted in the spark plug port, and protrudes into the combustion chamber. Upon the compression stroke, the piston makes contact with the rod and pushes it out of the chamber, leaving it at the maximum extent of piston travel. With the rod tip located at maximum piston ascent, the piston makes contact with it only at top dead center and completes the light bulb's electrical circuit on subsequent crankshaft rotations. This device requires a precision sliding surface between the slidable rod and the spark plug port mount, which is expensive to manufacture. This device also requires two people.
U.S. Pat. No. 4,263,868 shows a top dead center detector which comprises an air check-valve mounted in the combustion chamber's spark plug port. As the piston ascends to top dead center, the check valve opens and vents the chamber. When the piston continues past top dead center, the valve closes and seals the chamber. With the chamber sealed, the piston's descent past top dead center is halted by the vacuum thus created. This type of detector is necessarily inaccurate because the vacuum is created by the piston's descent, and so the piston must move substantially past top dead center before a vacuum sufficient to stop the piston is created.
Thus it would be advantageous to have a simple, inexpensive device that could be used by one person to accurately determine top dead center; could be manufactured at a low cost, is light weight, small and of simple construction; would be capable of easily detecting when the piston of an automobile engine is at the top dead center position; and would allow easy perception of the top dead center position of the piston of an automobile engine.